Control of gaseous pollutants such as hydrogen sulphide, carbon monoxide, ammonia, oxides of nitrogen, chlorine, formaldehyde, urea, volatile organic compounds etc. is normally required for environmental, corrosion, health and safety reasons. It is known in the art that gas mixtures containing one of more of these pollutants can be passed through filtration particulate material with chemical reactants which absorb, adsorb and/or react chemically with the pollutants to remove them from the gas mixture. Normally, filtration particulate material comprises an inert porous carrier with a large surface area for adsorption or for carrying chemical reactants.
It is further known in the art that certain pollutants can be removed by oxidation with permanganate. Permanganate containing filtration particulate material is disclosed in U.S. Pat. No. 6,004,522. Alkaline salts are also used in filtration particulate material to remove certain pollutants from a gas mixture. A small portion of free water needs to be present on the carrier to allow ionisation of the permanganate salt and/or other salts and to facilitate transfer of the ions to and from the reaction zone of the particulate matter. It will be appreciated that the higher the effective permanganate portion carried on the carrier, the more effective the particulate matter. However, the particulate matter is usually in the form of relatively dry granules or pellets and the free water therefore limited which, in turn, limits the portion of ionised permanganate and/or other salts. Non-ionised permanganate salts tend to crystallize and clog the pores of the carrier, which decreases the particulate material's efficacy. Known ways of increasing free water on the carrier are to use a hydrophilic carrier and/or to add a hygroscopic salt to the carrier. U.S. Pat. No. 6,004,522 discloses the use of sodium bicarbonate as a hygroscopic salt, however elevated levels of sodium bicarbonate also clogs the pores of the carrier and contributes in the formation of a hard medium, which decrease the particulate material's efficacy. This alkaline salt also contributes to the removal of acidic gases from a gas mixture. U.S. Pat. No. 6,004,522 puts forward the theory that the hygroscopic ionisation of the permanganate allows migration of the permanganate ions from inside the carrier media to the outside, as the permanganate on the surface of the carrier media is chemically reduced, in use.